Method and apparatus for sensing the presence of threads on a surface

ABSTRACT

The method of determining the presence or absence of threads on a surface relies upon the difference in back pressure sensed by the probe of a fluidic system. Back pressure will be greater when the probe is inserted into an unthreaded bore or encompasses an unthreaded stud and will trigger an output indicating that no threads are present. The apparatus for determining the presence or absence of threads on an object has no moving parts and includes a probe, a proportional center dump fluidic element connected to the probe and to a source of pressure, and a fluidic Schmitt trigger connected to amplify the output of the proportional element when the predetermined condition is sensed. Since the system operates on the difference in back pressure fed by the probe to the porportional element, it can be calibrated to generate an output signal indicating higher back pressure due to the absence of threads in a bore or on a stud.

United States Patent [191 J urkiewicz [451 Feb. 26, 1974 [75] lnventor:Walter J. Jurkiewicz, Philadelphia,

[73] Assignee: Robertshow Controls Company,

Richmond, Va.

22 Filed: Feb. 18, 1972 21 App1.No.:227,538

[52] US. Cl 73/37.5, 73/37.9, 116/70, 137/831 [51] Int. Cl. G0lb 13/22[58] Field of Search. 116/114, 65, 70, 117; 73/37.5, 73/37.9, 45.1;137/831, 827, 229, 830;

[56] References Cited UNITED STATES PATENTS 3,423,990 l/1969 Martin73/45.l 3,584,501 6/1971 Marradi 73/45.1 3,662,704 5/1972 Dega 116/70Primary Examiner-Louis J. Capozi Attorney, Agent, or Firm-Anthony A.OBrien [5 7] ABSTRACT The method of determining the presence or absenceof threads on a surface relies upon the difference in back pressuresensed by the probe of a fluidic system. Back pressure will be greaterwhen the probe is inserted into an unthreaded bore or encompasses anunthreaded stud and will trigger an output indicating that no threadsare present.

The apparatus for determining the presence or absence of threads on anobject has no moving parts and includes a probe, a proportional centerdump fluidic element connected to the probe and to a source of pressure,and a fluidic Schmitt trigger connected to amplify the output of theproportional element when the predetermined condition is sensed. Sincethe system operates on the difference in back pressure fed by the probeto the porportional element, it can be calibrated to generate an outputsignal indicating higher back pressure due to the absence of threads ina bore or on a stud.

9 'Claims, 5 Drawing Figures PATENTED FEBZB I974 SHEET 10f 2 METHOD ANDAPPARATUS FOR SENSING THE PRESENCE OF THREADS ON A SURFACE BACKGROUND OFTHE INVENTION 1. Field of the Invention The invention relates to thegeneral field of testing for threads in a bore or on a stud and inparticular to a fluidic system having no moving parts. The deviceoperates basically as a back pressure sensor which senses the increasedback pressure caused by the absence of threads in a bore or on a stud.

2. Description of the Prior Art It has long been a problem in the fieldof manufacturing to determine whether or not a bore or a stud has beenthreaded and is ready to receive a screw, a bolt or a nut. While mosttapping machinery will correctly tap a bore, occasionally a bore willnot be threaded due to breakage of the tap or some other unforeseenevent. In a similar fashion a stud may not be threaded. Whenever anunthreaded bore or stud arrives at a station where it is to receive ascrew, bolt, or nut, a jamming of the machinery inevitably occursresulting in expensive delays while the stoppage is cleared.

The known devices for sensing threads in a bore or on a stud haveprimarily relied upon optical or visual systems which are rathercomplicated and expensive.

SUMMARY OF THE PRESENT INVENTION It is an object of the presentinvention to provide a method and apparatus for detecting the presenceof threads in a bore or on a stud which utilizes a fluidic system havingno moving parts and which, by back pressure sensing, accuratelydetermines when the bore or stud is not threaded.

It is another object of the present invention to employ a fluidic devicehaving a proportional center dump fluidic element attached to a probe insuch manner that increased back pressure developed in an unthreaded boreor by an unthreaded stud will result in an output indicative of thesensed condition.

It is still another object of the present invention to provide a fluidicdevice which will amplify to a suitable level the signal generated by anunthreaded bore or stud to thus indicate whether or not the bore or studis threaded.

It is also an object of this invention to provide a fluidic apparatusfor determining the presence of threads in a bore or on a stud, whichapparatus may be readily and economically produced.

The apparatus for sensing the presence of threads on a surface, such asin a bore or on a stud, includes a probe, a proportional center dumpfluidic element connected to the probe and to a source of pressurizedfluid, and a fluidic Schmitt trigger connected to amplify the output ofthe proportional element and provide an indication of the presence orabsence of threads. The probe, in the case of bores, is sized for aclose fit in the bore and has a radially directed opening. The probeused on studs is adapted to closely fit over that portion of the studwhich should be threaded. The apparatus is operated in such manner thatthe increased back pressure resulting from a lack of threads on the unitunder test will give an output indication of this condition.

Other objects and advantages of the present invention will becomeapparent from the following description of the preferred embodimenttaken in conjunction with the accompanying drawings.

FIG. 1 is a schematic diagram of a screw thread sensing device accordingto the present invention.

FIG. 2 is an enlarged section of a probe for use with the screw threadsensing device of FIG. 1 for sensing internal screw threads.

FIG. 3 is a section of the probe of FIG. 2 used with an unthreaded bore.

FIG. 4 is an enlarged section of a probe for use with the screw threadsensing device of FIG. 1 for sensing external screw threads.

FIG. 5 is a section of the probe of FIG. 4 used with an unthreaded stud.

DESCRIPTION OF THE PREFERRED EMBODIMENT The illustrated embodiment ofthe inventive thread sensing device shows it being used to determine thepresence of threads in a bore 10 of a product unit 12. However, asmentioned above, the device is equally suitable for detecting thepresence of threads on a stud when a suitable probe is utilized.

The device is formed by three elements, namely, probe 14, proportionalcenter dump fluidic element 16, and fluidic Schmitt trigger 18. Theillustrated probe 14 is positioned in bore 10 with a close fit and has aradially directed opening 20 in close proximity to the walls of thebore. The probe for detecting threads on a stud, which probe has notbeen illustrated, would simply be an open ended probe closely fittingover the stud to be examined. It is preferable for the above mentionedclose fit to be a wiping or brushing contact between the probe and thesurface being examined in order to obtain the most accurate results.

The proportional center dump fluidic element or proportional amplifier16 is of a known type and includes a housing 22 having a supply port 24and symmetrically arranged input ports 26, 28 and output ports 30, 32.The supply port 24 is connected to a source of pressurized fluid (notshown) through filtering means (also not shown) by conduit 34 having acalibrated fixed restrictor 36 therein. Conduits 38 and 40, includingfixed restrictors 42 and 44, respectively, are connected between conduit34 and input ports 26 and 28, respectively. Conduit 46 connects probe 14to conduit 38 and input port 26. Only one of the output ports 30, 32 isconnected to an input port of the Schmitt trigger 18 through conduit 48while the other output port is left open.

The fluidic Schmitt trigger 18 is also well known and has inputs fromconduits 48, 50, 52 and 54. A variable restrictor 56 is connected inconduit 50 and a fixed restrictor 58 is connected in conduit 54.Conduits 50 and 52 are connected to a source of pressurized fluid (notshown) through fixed restrictor 60. Conduit 54 is likewise connected tothe source. The output from the Schmitt trigger is taken at conduit 62.The fluidic Schmitt trigger has been shown schematically as a block butis a pneumatic switch with an adjustable trigger. It is an analog todigital device utilizing a series arrangement of three proportionalamplifiers, a bistable device and a terminal OR-NOR stage.

The probe 14 for sensing internal threads, as illustrated in FIG. 2, hasan external cylindrical surface 64 for contacting the internalcylindrical surface of bore 10 such that the only substantial passagefor fluid flow after exiting from a radially directed opening is throughthe grooves of the screw threads. The screw threads are cut into theinternal surface of the bore 10; and, thus, the diameter of the externalsurface 64 of the probe is substantially the same as the diameter of thebore 10 prior to cutting of the screw threads therein such that if noscrew threads are present in the bore, as shown in FIG. 3, the externalsurface 64 of the probe 14 will contact the unthreaded internal surfaceof the bore to substantially prevent fluid flow between the probe andthe bore.

A probe 14' for sensing external threads is illustrated in FIGS. 4 and 5and has an internal cylindrical surface 66 for contacting the externalcylindrical surface 67 of a stud 68 with an axial opening 70 at thebottom of the probe. Accordingly, when a stud 68 to be examined isinserted in opening 70, the only substantial passage for fluid flow isthrough the grooves in the screw threads; and, similar to probe 14 ifthe stud 68 is unthreaded as shown in FIG. 5, the internal surface 66 ofprobe 14 will contact the unthreaded external surface 67 of the stud tosubstantially prevent fluid flow between the probe and the stud.

The thread senser operates basically as a back pressure senser asfollows: pressurized fluid is fed to the proportional element 16 throughconduits 34, 38 and 40. Some of the pressurized fluid also flows throughconduit 46 to probe 14 and out through opening 20 for sensing internalthreads or to probe 14 and out through opening 70 for sensing externalthreads. The element 16 is balanced in this condition so that the flowand pressure at the output ports 30 and 32 is equal. As long as theopening of the probe is not blocked, the pressurized fluid will flow outof the bore via the grooves of the threads. The system will thus be in abalanced condition with no output.

When the probe 14 is inserted into an unthreaded bore, the flow of fluidfrom opening 20 will be restricted causing a back pressure to build up.This back pressure will be fed to input port 26 and cause theproportional amplifier to become unbalanced. In this condition a greaterfluid flow and pressure will appear at output port 32 than at outputport 30. The increased output from port 32 will be sensed by the Schmitttrigger 18 and amplified to produce an output signal indicating that thesurface being tested does not have threads. Similarly, when the probe14' is positioned over an unthreaded stud, the flow from opening 70 willbe restricted to increase the back pressure and produce an output signalindicating an absence of threads.

It is preferable for the pressurized fluid fed to this system to befiltered to 5 microns and to be as oil free as possible. The means foraccomplishing this filtering are well known and therefore have not beenshown. However, this filtering step is rather important for all fluidicsystems of this general type since the elements themselves have smallorifices which could be easily obstructed if the pressurized fluid isnot clean and oil free. Likewise the fluidic elements should beprotected from ambient air borne dust and debris which might impedeproper flow through the system.

The thread sensor may be calibrated by attaching an indicator orpressure guage to the output 62 of the Schmitt trigger 18. Clean, oilfree air should be fed to the system at a pressure of approximately PSI.At

this time the indicator or gauge could have any reading. The probeshould be properly positioned with respect to a known sample, eitherthreaded or unthreaded, and the variable restrictor 56 adjusted for thecorrect output reading. This step may have to be repeated several timesto insure the proper setting of the variable restrictor 56.

The above described embodiment is intended to be illustrative only andnot to limit the scope of the invention which may have manymodifications and embodiments within the spirit of the invention.

What is claimed is:

1. A method for determining the presence or absence of screw threads ona surface comprising the steps of directing a fluid toward the surfacesuch that the only substantial passage for the fluid is through thegrooves of the screw threads; and

sensing the back pressure of the fluid directed toward the surface todetermine the presence or absence of screw threads on the surface.

2. A method according to claim 1 wherein said sensing step includesbalancing a fluidic system for a back pressure existing when screwthreads are present on the surface and unbalancing the fluidic systemwhen the back pressure increases above the balanced back pressure inresponse to the absence of screw threads on the surface.

3. A method according to claim 1 wherein the surface is an internalcylindrical surface and said fluid directing step includes positioningan outer cylindrical surface of a probe having a radially directedopening in wiping contact with the internal surface and supplying fluidto the probe.

4. A method according to claim 1 wherein the surface is an externalcylindrical surface and said fluid directing step includes positioning acylindrical internal surface of a probe in wiping contact with theexternal surface and supplying fluid to the probe.

5. A fluidic device for determining the presence or absence of screwthreads on a surface, comprising fluidic probe means having surfacemeans for contacting the surface to be examined such that grooves of thescrew threads provide the only substantial passage for fluid and meansfor directing a flow of pressurized fluid toward the surface to beexamined; and

means for sensing back pressure developed at said probe means whereby anincrease in back pressure indicates the absence of screw threads 6. Afluidic device according to claim 5 wherein said sensing means includesa proportional center dump fluidic element.

7. A fluidic device according to claim 6 wherein said sensing meansincludes a fluidic Schmitt trigger connected to amplify an output ofsaid fluidic element.

8. A fluidic device according to claim 7 wherein said surface means ofsaid probe means is an external cylindrical surface and said fluiddirecting means includes a radially directed opening in said externalsurface.

9. A fluidic device according to claim 7 wherein said surface means ofsaid probe means is an internal cylindrical surface and said fluiddirecting means includes an axially directed opening in said probemeans.

1. A method for determining the presence or absence of screw threads ona surface comprising the steps of directing a fluid toward the surfacesuch that the only substantial passage for the fluid is through thegrooves of the screw threads; and sensing the back pressure of the fluiddirected toward the surface to determine the presence or absence ofscrew threads on the surface.
 2. A method according to claim 1 whereinsaid sensing step includes balancing a fluidic system for a backpressure existing when screw threads are present on the surface andunbalancing the fluidic system when the back pressure increases abovethe balanced back pressure in response to the absence of screw threadson the surface.
 3. A method according to claim 1 wherein the surface isan internal cylindrical surface and said fluid directing step includespositioning an outer cylindrical surface of a probe having a radiallydirected opening in wiping contact with the internal surface andsupplying fluid to the probe.
 4. A method according to claim 1 whereinthe surface is an external cylindrical surface and said fluid directingstep includes positioning a cylindrical internal surface of a probe inwiping contact with the external surface and supplying fluid to theprobe.
 5. A fluidic device for determining the presence or absence ofscrew threads on a surface, comprising fluidic probe means havingsurface means for contacting the surface to be examined such thatgrooves of the screw threads provide the only substantial passage forfluid and means for directing a flow of pressurized fluid toward thesurface to be examined; and means for sensing back pressure developed atsaid probe means whereby an increase in back pressure indicates theabsence of screw threads
 6. A fluidic device according to claim 5wherein said sensing means includes a proportional center dump fluidicelement.
 7. A fluidic device according to claim 6 wherein said sensingmeans includes a fluidic Schmitt trigger connected to amplify an outputof said fluidic element.
 8. A fluidic device according to claim 7wherein said surface means of said probe means is an externalcylindrical surface and said fluid directing means includes a radiallydirected opening in said external surface.
 9. A fluidic device accordingto claim 7 wherein said surface means of said probe means is an internalcylindrical surface and said fluid directing means includes an axiallydirected opening in said probe means.